Master cylinder for hydraulic braking system

ABSTRACT

A master cylinder for hydraulic braking system of an automotive vehicle comprising a hydraulic piston slidably fitted in the cylinder bore, a valve member operatively connected to the piston and normally spaced from a reservoir inlet of the master cylinder for controlling fluid communication therethrough, a stopper bolt normally spaced from the piston for limiting the most retracted position thereof. When residual hydraulic pressure remains within the master cylinder after the brake has been released, the piston is immediately shifted to its most retracted position due to residual pressure whereby any residual hydraulic pressure is released to the reservoir.

United States Patent Ochiai et al. [4 1 May 16, 1972 [s41 MASTERCYLINDER FOR HYDRAULIC 3,143,860 8/l964 Stelzer ..60/54.6 E BRAKINGSYSTEM 3,486,337 l2/l969 Tenniswood ....60/s4.6 E 3,488,959 H1970Tenniswood ..60/54.6 E 1721 Invenmm gg' g gfg f ga 3,412,556 1 1/1968Rihe et a1. 60/546 E 73 1 Assignee: Aisin Seiki Kabushiki Kaisha, KariyaCity, Primary Examiner-Edgar fieoshesan Oichi Pref., Japan AssistantExaminer-A. M. Zupcic Filed. on n 1970 Attorney-Pierce, Schefl'ler 8:.Parker [2 l] Appl. No.: 79,757 [57] ABSTRACT A master cylinder forhydraulic braking system of an automo- [30] F rei A li tio Pri it Datative vehicle comprising a hydraulic piston slidably fitted in thecylinder bore, a valve member operatively connected to the Oct. I8, 1969Japan ..44/83507 piston and normally Spaced from a reservoir inlet ofthe master cylinder for controlling fluid communication [52] {1.8.31therethmugh a stopper be normally spaced from the piston g fi E 54 g Efor limiting the most retracted position thereof. When residual l e oarc hydraulic pressure remains within the master cylinder after thebrake has been released, the piston is immediately shifted [56]References and to its most retracted position due to residual pressurewhereby UNITED STATES PATENTS any residual hydraulic pressure isreleased to the reservoir. 3,! [7,421 l/l 964 Stelzer ..60/54.6 E 2Claims, 2 Drawing Figures 3,662,552 1 2 MASTER CYLINDER FOR HYDRAULICBRAKING The master cylinder according to the present invention SYSTEMcomprises a hydraulic piston means slidably fitted in a master Thisinvention relates to a master cylinder for use in the hydraulic brakingsystem of a powered vehicle, for example a motor vehicle.

Conventionally, the master cylinder comprises the hydraulic pistonslidingly fitted within the master cylinder housing, the hydraulicchamber being constituted in the cylinder housing, a stopper bolt fordefining the retracted position of the hydraulic piston, an elasticvalve member operatively connected to the hydraulic piston forcontrolling fluid communication between the oil reservoir and the wheelbraking system via the hydraulic chamber of the master cylinder, aninlet port provided in the master cylinder housing for permitting thebraking fluid to flow therethrough from the oil reservoir to thehydraulic chamber, said valve member being axially separated from theinlet port by a suitable distance (d) when the brake is released.

This construction is not desirable because the residual hydraulicpressure within the hydraulic chamber will result in axially stretchingthe elastic valve member as much as the distance d to keep the inletport sealed even after the brake pedal has been released. The saidresidual hydraulic pressure is likely to exist within the hydraulicchamber of the master cylinder under the following conditions:

1. When repeated braking operations are made causing excessive fluid toflow from the reservoir into the hydraulic chamber.

2. When vapor lock of the braking fluid occurs due to the frequentlyrepeated braking operation which will cause the brake drum and the liketo heat up, resulting in increasing the volume of said braking fluid.

3. When using a the mechanical brake, together with the hydraulic brake,the volume of braking fluid within wheel cylinder is increased by movingthe piston of the wheel cylinder. When the mechanical brake is released,it causes excessive braking fluid to remain in the hydraulic chamber ofthe master cylinder since the simultaneously released pedal brake willconvey back to the oil reservoir only that braking fluid which waslimited by the preceding brake pedal stroke.

When residual hydraulic pressure is locked within the hydraulic chamberof the master cylinder even after the brake pedal has been released, thevalve member made from a resilient material is stretched so that theport through which hydraulic pressure is to be conveyed back to the oilreservoir from the wheel braking system and master cylinder chamber iskept closed. As a result, a braking force due to the said residualhydraulic pressure is applied to the wheel braking system even after thefoot-operated brake has been fully released.

In order to overcome the above drawbacks, there has been proposed amaster cylinder structure in which the valve member is considerablyseparated from the compensating port in the master cylinder housing soas to be spaced therefrom even when residual hydraulic pressure isapplied to the valve member.

Such an arrangement, however, presented new problems. The greater thedistance is between the said inlet port of the master cylinder housingand the valve member, the longer the brake pedal stroke required uponapplication of the brakes. C'onsequently, there is required of thelonger stroke a brake pedal or a longer time to generate the increasedhydraulic pressure in the master cylinder so as to accomplish braking.

Therefore, the principal object of the invention is to provide a new andimproved master cylinder for a hydraulic braking system in which noresidual hydraulic pressure remains within the master cylinder after thebrakes have been released.

Another object of the invention is to provide a master cylinder for ahydraulic braking system in which the brake pedal stroke for applyingthe brakes is not elongated.

A further object of the invention is to provide a master cylinder for ahydraulic braking system which is simple in construction and economicalto manufacture.

cylinder bore and provided with a shoulder, hydraulic chamber meansprovided in the cylinder bore, a valve member operatively connected tosaid piston means for controlling fluid communication between an oilreservoir, and a wheel braking system via a port in the master cylinderbore, and stopper means normally spaced from the shoulder of said pistonmeans by a suitable distance, the retracted position of said pistonmeans being normally defined by a valve rod connected to said valvemember at its one end and to said piston means at its other end, themost retracted position of said piston means being defined by saidstopper means when residual hydraulic pressure remains within saidhydraulic chamber means.

In order to afford a clearer understanding of this invention a specificembodiment thereof will now be described with reference to the attacheddrawings, in which:

FIG. 1 is a sectional view of the master cylinder taken through thecenter of the master cylinder in its retracted or brake releasedposition; and

FIG. 2 is a fragmentary enlarged sectional view of FIG. 1 showing themaster cylinder in its most retracted position due to the residualhydraulic pressure.

Referring to the drawings, the tandem master cylinder 10 comprises acylinder housing ll and a cylinder bore 12 within which a first piston13 and a second piston 14 are slidingly and sealingly fitted. The firstpiston 13 is slidable through an opening 15 in a closure member 16 whichcloses the open end of the cylinder bore 12, there being two seals 17and 18 to prevent fluid leakage through the opening 15 and across theouter diameter of the closure 16. A snap ring 19 fitted within the slotof the housing 11 defines the retracted position of the first piston 13.A coil spring 20 is compressed between a shoulder 21 formed integrallywith the second piston 14 and a collar spring retainer 22 held at themost reduced diameter portion 24 of the first piston 23 by a snap ring25. At the reduced diameter portion 26 of the first piston 13, there issecurely attached a sealing cup 27.

The second piston 14 is sealed by two seals 28 and 29 whereby there isprovided a primary hydraulic chamber 30 between the first and secondpistons, while there is also provided a secondary hydraulic chamber 3]between the second piston 14 and an end wall 32 of the housing 11. Theprimary chamber 30 is connected via an outlet port 33 to one wheelbraking system via a compensating port 34 to a primary oil reservoir(not shown). The secondary chamber 31 is connected via an outlet port 35to the other wheel braking system and via a compensating port 36 to asecondary oil reservoir (not shown). The end wall 32 of the cylinderhousing is apertured to form the said compensating port 36.

An on-off control valve 37 made from a rubberlike material and adaptedfor cooperation with the compensating port 36 is normally spaced fromthe end wall 32 by a distance d in the conventional way and is fixed ona carrier member 38 which passes slidably through a guide opening 39formed in a valve guiding member or valve casing 40, said valve casing40 being shaped into a flanged cup and formed with a plurality of radialgrooves 41 which serve as oil passage means for hydraulically connectingthe compensating port 36 to the secondary hydraulic chamber 31. Thecarrier 38 is formed integrally with an axially extending rod 42 which,together with the carrier 38, is urged resiliently leftward by a spiralspring 23 interposed between the valve casing 40 and the valve carrier38 and is provided with an enlarged end 43 slidably fitted with in ablind bore 44 of the second piston 14.

A return spring 45 is kept in precompressed state between the valvecasing 40 and a cup-shaped retainer 46, said retainer being securelymounted on the left end of the second piston 14 and provided at its headportion with a guitar-shaped opening 47 to receive the axial rod 42. ltwill be seen that the rod 42 passes slidably through the opening 47 ofthe retainer 46 but the enlarged end 43 is checked thereby to preventthe rod from slipping out of the blind bore 44. It should be furthernoted that the return spring 45 has a spring strength equal to orstronger than the coil spring 20, but the retracted position of thesecond piston 14 is normally defined by the valve rod 42 engaged withthe cup retainer 46.

The right hand end of the first piston 13 is formed with a deep axialrecess 48 the apex of which is kept in pressure contact with the innerend of a push rod 49, said rod being mechanically connected to aconventional foot-operated brake pedal (not shown).

A stopper bolt 50 is screwed in the cylinder housing 11 and projectedinto the primary hydraulic chamber 30 at 51. The projection 51 is spacedfrom the shoulder 21 of the second piston 14 by distance D when themaster cylinder is assembled or when no residual hydraulic pressureremaining in the secondary chamber 31, said projection being adapted forengagement with the shoulder 21 thereby defining the most retractedposition of the second piston 14 due to residual hydraulic pressurewithin the secondary chamber 3].

In operation, when the operator depresses the foot-brake pedal so as tomove the push rod 49 in the left direction in FIG. 1, the firsthydraulic piston 13 is also moved to the left against the action of thespring 20 so that the compensating port 34 is blocked by the sealing cup27. Thus the hitherto established hydraulic connection between theprimary reservoir and primary hydraulic chamber is interrupted, thehydraulic pressure prevailing therein being suddenly increased. Thisincreased hydraulic pressure is then conveyed from the chamber 30through the outlet 33 to one of the wheel braking systems. The secondpiston is also moved to the left against the action of the return spring45 due to the increased hydraulic pressure in the primary chamber andthe exerting force of the coil spring 20. With the movement to the leftof the second piston 14, the retainer 46 carried thereby will performthe same amount of axial movement as the piston, thus the pressurecontact between the cup-shaped retainer 46 and the enlarged end 43 ofthe rod is released. Therefore, the valve member 37 is moved to the leftby the conical spring 23 so that the hitherto established communicationbetween the secondary oil reservoir and secondary chamber isinterrupted. The hydraulic pressure in the secondary chamber 31 is thusincreased and conveyed to the other wheel braking system through theoutlet port 35.

When the operator releases his foot pressure from the brake pedal, thefirst and second pistons are returned rapidly from their brake actuatingpositions to their original starting positions under the returningaction of the coil springs 20 and 45, respectively. When the firstpiston 13 is brought into its original starting position the fluidcommunication between the primary reservoir and primary chamber isreestablished since the sealing cup 27 is moved from the compensatingport 34 to the right together with the first piston, thus thepressurized fluid is conveyed back to the primary reservoir via port 33,the primary hydraulic chamber 30, and the compensating port 34.

ln the similar way, when the second piston is brought into its originalstarting position the fluid communication between the secondaryreservoir and secondary chamber is reestablished since the axial rod 42integral with the valve carrier 38 is moved to the right together withthe cup-shaped retainer 46, thus the pressurized fluid is conveyed backto the secondary reservoir via the port 35, the secondary chamber 31,and the compensating port 36.

When hydraulic pressure remains as residual hydraulic pressure withinthe secondary chamber 31 even after the brake pedal has been released,for instance, afier repeated braking operations have been made, thesecond piston will be moved to the right a distance D until it engageswith the projection 51 of the stopper bolt 50 as is shown in FIG. 2,causing the rod 42 to move to the right. The valve member 37 is thusseparated from the end wall 32 of the cylinder housing by the distance dplus D whereby objectionable residual hydraulic pressure causing thevalve member to axially stretch is not a plied.

Although a tandem master cylinder is describe as an embodiment of thisinvention, it should be recognized that the invention is also applicableto a master cylinder having a single hydraulic piston.

What we claim is:

l. A master cylinder for a hydraulic braking system comprising acylinder housing provided with a bore, piston means slidably andsealingly mounted within said bore and provided with a circumferentialshoulder at one end thereof, said piston means and cylinder housingforming a hydraulic chamber which communicates with a wheel brakesystem, port means provided in the end wall of said cylinder housing andcommunicating with a reservoir, a valve member composed of an elasticmaterial operatively connected to the other end of and having a smallercross-sectional area than said piston means for controllingcommunication through said port means, said valve member being normallyaxially spaced from said port means when the brakes are released andthere is no residual hydraulic pressure within said hydraulic chamber, afixed abutment stopper means provided in the bore of said cylinderhousing normally spaced an axial distance from and adjacent the shoulderof said piston means when in the normally released piston, said stoppermeans cooperating with the shoulder to limit additional axial movementof said piston means and valve member caused by possible residualhydraulic pressure remaining in said hydraulic chamber when the brakesare released, to ensure opening of said port means by said valve memberto release the residual hydraulic pressure to the reservoir.

2. A master cylinder as claimed in claim 1 and further comprising avalve carrier for supporting said valve member and an axial rod securedat one end to said valve carrier, its other end being slidably receivedin said piston means and movable therewith when said piston means ismoved axially by residual hydraulic pressure toward said stopper means.

t t 1 i l Paton: No. 3, 55 Dated May 16, 1971 Inventor) CHIAKI OCHIAIand TAKASHI FUJII I: is certified aha: :ro: appears in theabove-identified pace-.11: and :na; said Letters Patent; are herebycorrected as s'aowa below:

" .CiaiJn [line 18, toe' word -"p1ston"- I Q l y I posflfioion I The; iast rgame .of the. second inventor is Ipcoi roofc ly pol'led "Fuji" oshould be "FUJII" i aafighseai'dith s 25th day fauna-972.

EDWARD MmmTm-B'Jmffnumm GQTTSCHALK At'testin g' Offic a Commissioner of:Pgatents

1. A master cylinder for a hydraulic braking system comprising acylinder housing provided with a bore, piston means slidably andsealingly mounted within said bore and provided with a circumferentialshoulder at one end thereof, said piston means and cylinder housingforming a hydraulic chamber which communicates with a wheel brakesystem, port means provided in the end wall of said cylinder housing andcommunicating with a reservoir, a valve member composed of an elasticmaterial operatively connected to the other end of and having a smallercross-sectional area than said piston means for controllingcommunication through said port means, said valve member being normallyaxially spaced from said port means when the brakes are released andthere is no residual hydraulic pressure within said hydraulic chamber, afixed abutment stopper means provided in the bore of said cylinderhousing normally spaced an axial distance from and adjacent the shoulderof said piston means when in the normally released piston, said stoppermeans cooperating with the shoulder to limit additional axial movementof said piston means and valve member caused by possible residualhydraulic pressure remaining in said hydraulic chamber when the brakesare released, to ensure opening of said port means by said valve memberto release the residual hydraulic pressure to the reservoir.
 2. A mastercylinder as claimed in claim 1 and further comprising a valve carrierfor supporting said valve member and an axial rod secured at one end tosaid valve carrier, its other end being slidably received in said pistonmeans and movable therewith when said piston means is moved axially byresidual hydraulic pressure toward said stopper means.